Need pKa of pyrophosphoric acid

[Lilienthal]

I need the pK_as of pyrophosphoric acid = H4P2O6 or an ester thereof. Unfortunately I don't have a book here, but I have already checked Google and ClearLight's link   .
Thanks  

[GC_MS]

0.9 - 2.0 - 6.6 - 9.4

http://216.239.33.100/search?q=cache%3A4FpZn1kqkJcC%3Aicg.harvard.edu/~chem206/Fall_2001/lectures/18_Acid_Based_Properties_of_Organic_Molecules/pKa_compilation.pdf+pka+%2B+pyrophosphoric&hl=en&ie=UTF-8

Another page gives 0.9, 1.5, 5.8, 8.2 though...

WOMAN.ZIP: Great Shareware, but be careful of viruses...

[Lilienthal]

Thanks a lot, good find. Google seems to have problems with * as a wildcard!?